It only takes up work time unless the machine breaks down completely (maintenance falls to 0), in which case it costs a component.

note that machines have a risk of breakdown inversely proportional to maintenance level; the lower maintenance is, the higher the risk of a breakdown (starting at 50% maintenance IIRC). At 0% maintenance, breakdowns are _very_ likely. Only when a breakdown occurs do you need to use components to fix the machine, and maintenance is reset to 100% after a breakdown has occured.

@Fluffy That's what I want to know. I thought that breakdown would only happen when the maintenance drops to 0%...